Setting the output power of a transmitter in a transceiver at an optimum level is very desirable because it (1) helps to avoid the overloading of a receiver, (2) provides the link optimization of an optically amplified WDM communication system, and (3) reduces power consumption. The optimum output power of the transmitter depends solely on each system in which the transceiver is operating. Here all the communication systems are grouped as follows: (1) communication systems without optical amplifiers, and (2) optically amplified WDM communication systems.
For the communication systems without optical amplifiers, it is not rare that a service provider encounters occasions of deploying a transceiver whose transmitter output power set by the transceiver supplier might overload the receiver at the other end of the communication system when the link loss is much smaller, for example, a very short span of the fiber link, than the typical link budget of the transceiver. To avoid the overloading, an optical attenuator of fixed attenuation is frequently inserted just before the receiver, which is an extra expenditure.
On the other hand, when the link loss of the communication system is a little bit bigger than expected, the service provider sometimes needs to increase slightly the output power of the transmitter, for example, by around 1 dB while the increase is within the limit of the specification of the transmitter.
For the optically amplified WDM communication systems, it is a common practice to execute the optimization of the link composed of multiple transceivers running at different wavelengths, optical multiplexes (MUX's), optical amplifiers, link fibers, and optical demultiplexers (DEMUX's), through tuning of an individual channel transceiver. Particularly, the output power of the transmitter of each transceiver is optimized/equalized such that one channel, for example, would not predominantly determine the overall performance of the link with optical amplifiers.
For the reduction of power consumption, setting the output power of the transmitter at the optimum rather than at the higher output power typically set at the factory of the transceiver supplier will reduce significantly the power consumption of a communication system where many transceivers are used through the accumulation in saving of small amount of power consumption of each transceiver; this will also reduce the power consumption in cooling the communication system at the central office (CO) of the service provider which effectively saves the capital expenditure (CAPEX) and operating expenditure (OPEX) of the service provider; this will also prolong the life span of this communication system, particularly the transmitter of the transceiver.
A transceiver will, in general, be benefitted when it is equipped with the adjustability of the output power of a transmitter in the transceiver as described above. Because (1) a communication system consists of, at least, two transceivers where the transmitter of one transceiver is transmitting a signal to the receiver of another transceiver, and (2) the optimum output power of the transmitter depends solely on each system in which the transceiver is operating, the controllability of the output power of the transmitter in one transceiver by another transceiver will be a desirable feature. This is particularly true if two transceivers are physically separated far away from each other. In other words, a remote controllability of the output power of the transmitter of one transceiver by another transceiver will be very valuable, considering the facts that (1) the adjustment of its output power can be executed by the technician at the CO where all the necessary test equipments are accessible easily and (2) another technician does not have to be present simultaneously at the site of the transceiver which is in need of adjustment of its output power; this will save a lot of capital and operating expenditures (CAPEX and OPEX) by the service provider/operator.